The objectives of this research are to make use of earlier studies of thiamin, thiamin pyrophosphate and their derivatives and analogues to determine the relationship of the structure of these compounds to the coenzymatic function and the nature of the interaction of the appropriate apoenzymes with the coenzyme, divalent metal cations and substrates. Specific problems and areas to be attacked include the following: 1. Ternary complexes of transketolase wit thiamin-PP and Mn 2 ion will be studied by various NMR and EPR techniqes to determine what kind of interactions are involved, in an attempt to explain the quasi-irreversibility of coenzyme binding; 2. C13-NMR studies of 2-(alpha-hydroxybenzyl)-thiamin will be carried out to determine whether the conformation in solution of such derivatives is the same as that found by x-ray crystallography; 3. Analogues of thiamin will be synthesized for use in studies of the mechanism of catalysis by thiamin. Thiamin deficiency states occur in chronic alcoholism, and disorders of thiamin function are associated with neurological disease, in particular Wernicke's encephalopathy which is a late manifestation in prolonged alcoholism, and Leigh's syndrome or subacute necrotizing encephalomyelopathy which is a fatal neurological disease of infants and young children. Better understanding of thiamin function may aid in the understanding of these diseases.